1. Field of the Invention
The present invention relates to an image-processing device and an image-processing method.
2. Description of the Related Art
Various techniques for embedding special information in image data have been proposed, for example, to prevent the image data from being copied in an unauthorized manner and/or falsified. There is a technology referred to as the digital-watermark technology, which is used to embed additional information in electronic data corresponding to an image including a photograph, a painting, etc., where the additional information includes, for example, information about the name credit and/or use permission of the electronic-image data. In recent years, the technology of distributing image data where the additional information is embedded so that the additional information is visually unobtrusive via a network such as the Internet has become more standardized.
Further, the technology of determining the type and/or number of a printing device which printed an image on the basis of a printed matter such as an image printed on a piece of paper has also been studied. The determination technology is used to prevent a bill, a stamp, a negotiable instrument, etc. from being forged, as the quality of an image attained by an image-forming device including a copier, a printer, etc. is improved.
According to the above-described technology, for example, the additional information is often embedded in part of image data, where the part corresponds to a color-difference component with low visual sensitivity and the high-frequency part of a saturation component. However, it is difficult to embed large-capacity information such as sound information in image data during printing by using the above-described technology so that the large-capacity information is unobtrusive.
Further, the method of artificially generating the combination of quantization values that do not occur through ordinary pseudo-halftoning by using a texture occurring through an error-diffusion method, and embedding code data generated on the basis of the quantization values is known, as another example of the above-described technology. According to the above-described embedding method, the visual quality of image data where the code data is embedded hardly differs from that of original image data, even though the geometry of the texture of the image data where the code data is embedded is microscopically changed. Further, according to the above-described embedding method, different signals can be easily multiplexed on one another by changing the quantization-threshold value while executing the error-diffusion method.
Here, an image-processing system configured to embed the additional information in arbitrary image data, print the image data so that a printed matter is generated, and retrieve the embedded additional information from the printed matter will be described. FIG. 1 is a block diagram showing the configuration of an image-processing device configured to embed the additional information in arbitrary image data and print the image data.
According to the image-processing device, arbitrary multi-level gray scale image information is input via an input terminal 191, and additional information which will be embedded in the image information is input via an input terminal 192. The additional information includes various types of information about a copyright, photographing date and time, a photographing location, a photographer, etc. relating to the image information input from the input terminal 191 and/or sound information, text information, etc. that are not relating to the image information.
An additional-information-multiplexing unit 193 embeds the input additional information in the input image information so that the additional information is visually unobtrusive. Namely, the additional-information-multiplexing unit 193 divides the input image information into N×N-pixel blocks, and embeds the additional information in each of the blocks.
A printer 194 prints the image information where the additional information is embedded onto a print medium, and outputs a printed image 195. The printer 194 is configured, as an ink-jet printer, a laser-beam printer, etc., which can represent gray scale through pseudo-halftoning.
FIG. 2 is a block diagram showing the configuration of an image-processing device configured to retrieve the additional information embedded in the image information shown in the printed image 195, which is the output of the image-processing device shown in FIG. 1.
The image-processing device acquires the image data corresponding to the image information printed on the print medium through an image scanner 201. Upon receiving the image data, an additional-information-separation unit 202 detects an image area where the additional information is embedded by performing known image processing. According to a representative detection method, the boundary between a non-image area and an image area is detected based on the color-density difference. After detecting the image area, the additional-information-separation unit 202 separates the additional information embedded in the detected image area, and outputs the separated additional information to an output terminal 203.
However, the above-described image-processing system has the following problems.
First, according to the image information input from the input terminal 191, it is often difficult to detect the boundary between the non-image area and the image area according to the method of detecting the image area on the basis of the color-density difference shown in the image data. Since the additional information is unobtrusively embedded in the image data where the above-described boundary is shown with poor clarity, the image area should be defined with precision. For example, when reading the printed image 195 through the image scanner 201, the image area should be subjected to trimming before setting. However, it is often difficult for the user to determine which area of the image area should be trimmed, so as to set the image area.
Further, the input image is divided into two or more N×N-pixel blocks, and information obtained by dividing the additional information is multiplexed on each of the blocks. Therefore, the additional-information-separation unit 202 should grasp the area of each of the blocks with an error of about few pixels at the maximum. When the error is increased, the precision with which the additional information is detected is significantly decreased, which makes it difficult to correctly extract the additional information.
In the past, the method of arranging reference marks around the image area where the additional information is embedded at predetermined intervals and printing the image data has been used, so as to solve the above-described problems. According to the above-described method, it becomes possible to read the printed image by using an image scanner, detect the reference marks from the read image information, correct distortion according to the reference marks, and detect the block area with high precision.
FIG. 3 shows the overview of a printed matter obtained through the above-described method. Image information 231 is shown inside an area indicated by oblique lines, the area being shown on a print medium 232. Then, reference marks 233 are shown so that the image information 232 is surrounded by the reference marks 233. By forming the reference marks 233 on the print medium 232, it becomes possible to detect the reference marks 233 and detect an N×N-pixel block 234 with high precision.
In recent years, the functions of image-forming devices including a copier, a printer, etc. have been improved. Therefore, the function of performing borderless printing for an image picked up by an image-pickup device such as a digital camera has been provided, and the number of users performing the borderless printing has increased. There are many printers configured to make the size of image data for printing larger than that of a print medium and print the image data so that the border of the image data is cut off, whereby the borderless printing is achieved.
If a device implementing the borderless printing by cutting the border of an image attempts to print the reference marks around the image area, so as to detect the image area where the additional information is embedded, the reference marks may be cut off.
FIG. 4 shows an example where the borderless printing is performed for the printed matter obtained through the above-described method. In that case, the reference marks 233 arranged at the predetermined intervals around the image information 231 are positioned outside the print medium 232 so that the reference marks 233 are not formed. Since the reference marks 233 are not shown, it is difficult to detect the N×N-pixel block 234 with high precision. That is to say, the method of arranging the reference marks 233 around the image area is not appropriate for performing the borderless printing.
Of course, if the size of the print medium 232 is made to agree with that of image data for printing and the image data is printed so that the position of the print medium 232 does not deviate from the position of the image data, it becomes possible to print the image data including the reference marks 233 on the print medium 232. However, the mechanism of the printer makes it difficult to print the image data so that the position of the print medium 232 does not deviate from the position of the image data.
Further, the technology of embedding the additional information in an area of the same size as that of a printed-image area, detecting the edge line of the printed-image area, and detecting the additional information embedded in the area of the same size as that of the printed-image area has been available.
FIG. 5 shows the overview of a printed matter obtained through the above-described technology. A printed-image area is defined on the print medium 232 and the image information 231 is formed. The N×N-pixel block 234 is set according to the size of the image information 231. Therefore, if the edge of the image information 231 (the edge line of the printed-image area) can be detected, the N×N-pixel block 234 can be detected with high precision.
FIG. 6 shows an example where the borderless printing is performed for the printed matter obtained through the above-described technology. When the borderless printing is performed, the border of the image data is cut off. Therefore, even though the edge of the image information is detected from the printed image, the detected edge is different from that of the image information 231 which is not yet printed, which makes it difficult to detect the N×N-pixel block 234 with high precision.
Further, when data shown on the printed image is read, it is desirable for the user that the data is read even though the user is not aware of the orientation of the print image and the N×N-pixel block 234 is detected with high precision.
In another case, embedded information can be extracted irrespective of the block position and the orientation of a print medium by using a two-dimensional code such as QR Code (Registered Trademark). In the case where the two-dimensional code is used, however, the embedded information includes marker data visible to a person, which may affect the design of a photograph and/or a painting.